Question

我已经看到了一些如何实现这一目标的例子，但我仍然无法使其发挥作用。

我遵循了this示例，TextView在OnCreate中为空，当我旋转屏幕时。以下是我实施它的方法：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
    setContentView(R.layout.activity_image_viewer);

    displayFileName = (TextView) findViewById(R.id.displayFileName);

    //Getting the fileName
    Bundle extras = getIntent().getExtras();
    uri = extras.getString("uriAsString");
    Uri myUri = Uri.parse(uri);
    filename = uri.substring(uri.lastIndexOf("/") + 1);
    nameWitoutExtention = filename.substring(0, filename.lastIndexOf('.'));

    //Checking if Text was stored
    if (savedInstanceState != null) {
        CharSequence savedText = savedInstanceState.getCharSequence(KEY_TEXT_VALUE);
        displayFileName.setText(savedText);
    }

}

@Override
protected void onSaveInstanceState (Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putCharSequence(KEY_TEXT_VALUE, displayFileName.getText());
}

我想要达到的目的是将nameWitoutExtention设置为displayFileName，并在设备旋转时让文字保留。

我在文本上有一个空指针，这就是我尝试这个的原因，对我做错的任何帮助？

修改

这就是我目前的实施情况：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
    setContentView(R.layout.activity_image_viewer);

    displayFileName = (TextView) findViewById(R.id.displayFileName);

    if(savedInstanceState != null){
        CharSequence savedText = savedInstanceState.getCharSequence(KEY_TEXT_VALUE);

        //When displaying this toast the correct filename gets displayed
        //Toast.makeText(getApplicationContext(), savedText, Toast.LENGTH_LONG).show();

        displayFileName.setText(savedText+"");
    }
    else{
        //Getting the fileName
        Bundle extrsas = getIntent().getExtras();
        uri = extrsas.getString("selectedStudentVid");
        Uri mUri = Uri.parse(uri);
        filename = uri.substring(uri.lastIndexOf("/") + 1);
        nameWitoutExtention = filename.substring(0, filename.lastIndexOf('.'));
        displayFileName.setText(nameWitoutExtention);
    }

@Override
protected void onSaveInstanceState (Bundle outState) {
    super.onSaveInstanceState(outState);      
    outState.putCharSequence(KEY_TEXT_VALUE, displayFileName.getText());
}

我也按照@PorasBhardwaj

的建议尝试了onRestoreInstanceState()

我得到的例外是：

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference

Answer 1

尝试使用onRestoreInstanceState()回调方法获取已保存的数据。

@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
 // TODO Auto-generated method stub
 super.onRestoreInstanceState(savedInstanceState);
 CharSequence savedText = savedInstanceState.getCharSequence(KEY_TEXT_VALUE);
 displayFileName.setText(savedText);
}

根据官方文件。

大多数实现只会使用onCreate（Bundle）来恢复它们状态，但有时候在这里做完之后很方便初始化已完成或允许子类决定是否使用您的默认实现。

因此，为了获得最佳实践，请将您的视图层次结构保留在onCreate中，并在onRestoreInstanceState中恢复之前的状态。

Answer 2

尝试这样做：

//Checking if Text was stored
 if(savedInstanceState != null){
       CharSequence savedText = 
      savedInstanceState.getCharSequence(KEY_TEXT_VALUE);
      displayFileName.setText(savedText + "");
 }
else{
 //Getting the fileName
Bundle extras = getIntent().getExtras();
uri = extras.getString("uriAsString");
Uri myUri = Uri.parse(uri);
filename = uri.substring(uri.lastIndexOf("/") + 1);
nameWitoutExtention = filename.substring(0, filename.lastIndexOf('.'));
}

你做错了什么。每当方向改变时，它再次从额外值获得值，在旋转改变之后为null，并且它将相同的值传递给它。这就是你获得例外的原因。试试这个希望它会对你有帮助。

旋转时保存和恢复文本

2 个答案: